1. Field of the Invention
The present invention relates to flow switches and particularly to an improved switch assembly which has two operating states reflecting whether liquid is flowing or not.
2. Description of the Prior Art
The closest known prior art is disclosed in the above identified cross references. The present invention forms an improvement over that prior art.
The apparatus disclosed in the patents relate to control of pumps, burners, alarms, meters, or similar devices where the flow of liquid in a pipe is of critical significance. Some of the more common fields of application are found in the starting or stopping of a burner in commercial water heaters, the control of a compressor in an air circulation system, the energization of a standby pump upon failure of a primary pump, or with a flow indicator in liquid process systems and the like.
The prior art switches disclosed in the patents were adapted to be fitted in a T-connection associated with a horizontal pipeline where a horizontal run of liquid was encountered. Paddle means were embodied therein for moving an actuation arm which pivoted about an axis located exteriorly of the pipeline and sealed therefrom by a flexible metal bellows. The actuating arm carried a suitable finger portion at its upper end for engaging the plunger of an electrical control switch and could be arranged to maintain the switch contacts open or closed in response to the flow of fluid through the pipeline with which it was associated. Other features included a multi-part paddle system which readily adapted the same to various diameter pipelines and an adjusting system for regulating the throw of the paddle required to operate the switch contacts. Additional means were provided for adjusting the sensitivity of the paddle means to the flow or velocity of fluids in the pipeline.
Shortcomings of this prior art result from the use of a metal bellows which is relatively insensitive to pressure changes. This bellows has been supplanted in embodiments of the present invention by a more flexible membrane, thereby reducing complexities in manufacturing while providing more than an equivalent amount of sealing and providing a more sensitive response to pressure and flow variations.
The copending application referred to above contains a disclosure of an improved flow switch which affords advantages over the patents. However, embodiments of this improved switch have included adjustment means and other means which have increased complexity and cost to a greater degree than has proven to be desirable, or necessary, for use in many applications.
A disadvantage with the embodiments shown in the application, as well as in the patents referred to above, has resulted from the use of particular bearings about which the lever arm turns. These bearings have had a rather rough finish which is inherent in their manufacture and this has resulted in poor wearing qualities attended by poor control of the motion of the lever arm and poor regulation of the switch, particularly after prolonged use and where two or more switches are controlled by a single lever arm.